sc_star_image.h File Reference

Star image processing functions. More...

Go to the source code of this file.

Classes
struct	gaussian_fit_s
	Structure for Gaussian fit. More...
struct	gaussian_xyfit_s
	Structure for X/Y Gaussian fit. More...
struct	star_blob
	Blob in a star image. More...

Typedefs
typedef struct gaussian_fit_s	gaussian_fit_t
	Structure for Gaussian fit.
typedef struct gaussian_xyfit_s	gaussian_xyfit_t
	Structure for X/Y Gaussian fit.

Functions
ml_matrix	vm_to_intensity (ml_matrix v)
	Converts visual magnitude to intensity. More...
ml_matrix	intensity_to_vm (ml_matrix i)
	Converts intensity to visual magnitude. More...
double	vm_to_intensity (double v)
	Converts visual magnitude to intensity. More...
double	intensity_to_vm (double i)
	Converts intensity to visual magnitude. More...
void	index_to_sub (int r, int c, int k, int *kR, int *kC)
	Matrix index to subscripts.
ml_matrix	centroid_COM (const ml_matrix &p, double threshold, int n)
	Find centroids in a pixelmap using the center of mass method. More...
ml_matrix	coarse_centroid_COM (const ml_matrix &p, double threshold=0.0, int n=5)
	Find centroids in a pixelmap using blobify & center of mass method. More...
int	edge_correction (int k0, int kC, int m)
	Edge correction. More...
ml_matrix	zodiacal_light (const ml_matrix &r, const ml_matrix &beta)
	Zodiacal light. More...
double	zodiacal_light (double r)
	Zodiacal light. More...
void	apply_threshold (ml_matrix &x, double b=-1.0, double T=0.0)
	Star image noise processing function. More...
ml_matrix	fit_gaussian (const ml_matrix &pixels, const ml_matrix &r0, gaussian_xyfit_t &data)
	Fit symmetric Gaussians to a star image. More...
std::list< star_blob >	Blobify (const ml_matrix &pixels, int minPix=4)
	Blobify a pixelmap. More...

Detailed Description

Star image processing functions.

Function Documentation

vm_to_intensity() [1/2]

ml_matrix vm_to_intensity

(

ml_matrix

v

)

Converts visual magnitude to intensity.

Converts visual magnitude to intensity.

Parameters

v	Visual magnitude

Returns

Intensity

Referenced by star_meas::SetStarData(), and zodiacal_light().

intensity_to_vm() [1/2]

ml_matrix intensity_to_vm

(

ml_matrix

i

)

Converts intensity to visual magnitude.

Converts intensity to visual magnitude.

Parameters

i

Intensity

Returns

Visual magnitude

vm_to_intensity() [2/2]

double vm_to_intensity

(

double

v

)

Converts visual magnitude to intensity.

Converts visual magnitude to intensity.

Parameters

v	Visual magnitude

Returns

Intensity

intensity_to_vm() [2/2]

double intensity_to_vm

(

double

i

)

Converts intensity to visual magnitude.

Converts intensity to visual magnitude.

Parameters

i

Intensity

Returns

Visual magnitude

centroid_COM()

ml_matrix centroid_COM	(	const ml_matrix &	p,
		double	threshold,
		int	n
	)

Find centroids in a pixelmap using the center of mass method.

Find centroids in a pixelmap using the center of mass method.

Parameters

p	pixel values (:,:)
threshold	threshold for including in the center of mass
n	size of the region of interest

Returns

locations of centroids in pixels (2,n)

References edge_correction(), and index_to_sub().

coarse_centroid_COM()

ml_matrix coarse_centroid_COM	(	const ml_matrix &	p,
		double	threshold,
		int	n
	)

Find centroids in a pixelmap using blobify & center of mass method.

Find centroids in a pixelmap using blobify & center of mass method.

The pixelmap is first thresholded to remove pixels below the background noise. The remaining pixels are then grouped in "blobs". Centroids are computed for the blobs using a center of mass method.

TODO parameter for minimum number of pixels in blobs TODO parameter or better way for calculating noise floor b

Parameters

p	pixel values (:,:)
threshold	threshold for including in the center of mass
n	size of the region of interest

Returns

locations of centroids in pixels (2,n)

See also

apply_threshold(), Blobify()

References apply_threshold(), and Blobify().

edge_correction()

int edge_correction	(	int	k0,
		int	kC,
		int	m
	)

Edge correction.

Edge correction.

Parameters

k0
kC
m

Returns

Referenced by centroid_COM().

zodiacal_light() [1/2]

ml_matrix zodiacal_light	(	const ml_matrix &	r,
		const ml_matrix &	beta
	)

Zodiacal light.

Used by imager functions. This is background noise.

Reference: R. Meissner, "Brightness Measurements of Stars and the Night-Sky with a Silicon-Photomultiplier-Telescope" Physikalischen Institut A, 9/2012.

Parameters

r	Distance from the sun (AU)
beta	Ecliptic latitude (rad)

Returns

Intensity (W/m^2/rad^2)

References PI, and vm_to_intensity().

Referenced by imager_model::update().

zodiacal_light() [2/2]

double zodiacal_light

(

double

r

)

Zodiacal light.

Zodiacal light.

Uses the worst-case beta.

Reference: R. Meissner, "Brightness Measurements of Stars and the Night-Sky with a Silicon-Photomultiplier-Telescope" Physikalischen Institut A, 9/2012.

Parameters

r	Distance from the sun (AU)

Returns

Intensity (W/m^2/rad^2)

References PI, and vm_to_intensity().

apply_threshold()

void apply_threshold	(	ml_matrix &	x,
		double	b,
		double	T
	)

Star image noise processing function.

Star image noise processing function.

Values in x below the threshold, T, will be set to zero. The sky background noise, b, will be subtracted from the remaining pixels.

p(p<T) = 0 p = p - b;

If b is less than zero, the mean will be calculated. If T is less than or equal to zero, it will be approximated as b + 2.5*sigma.

Parameters

x	Pixelmap
b	Sky background noise value, to be subtracted from pixels
T	Threshold value

Referenced by coarse_centroid_COM().

fit_gaussian()

ml_matrix fit_gaussian	(	const ml_matrix &	pixels,
		const ml_matrix &	r0,
		gaussian_xyfit_t &	data
	)

Fit symmetric Gaussians to a star image.

Fit symmetric Gaussians to a star image.

This should be a subarray containing a single star.

Parameters

pixels	Pixelmap
r0	Initial guess
data	Algorithm data results

Returns

Matrix with [x;y] center

References gaussian_fit_s::height, gaussian_xyfit_s::height, gaussian_fit_s::iter, gaussian_xyfit_s::iter, gaussian_fit_s::status, gaussian_xyfit_s::status, gaussian_fit_s::std_dev, and gaussian_xyfit_s::std_dev.

Blobify()

std::list< star_blob > Blobify	(	const ml_matrix &	pixels,
		int	minPix
	)

Blobify a pixelmap.

Blobify a pixelmap.

A bounding box is stored along with the indices of the pixels in the blob. The pixelmap is assumed to be thresholded so that most of the pixels are zero and only those nonzero pixels will be grouped into blobs. Currently only single-pixel stars are removed. The blobs are sorted in descending order by total counts.

TODO: set a cap on number or percentage of nonzero pixels.

Parameters

pixels

Returns

List of blobs

Referenced by coarse_centroid_COM().